Abstract—The influence of lactulose and inulin on rheological properties of fermented milk during storage was studied.Pasteurized milk, freeze-dried starter culture Bb-12 (Bifidobacterium lactis, Chr. Hansen, Denmark), inulin – RAFTILINE ® HP (ORAFI, Belgium) and syrup of lactulose (Duphalac ® , the Netherlands) were used for experiments. The fermentation process was realized at 37 o C for 16 hours and the storage of products was provided at 4 o C for 7 days. Measurements were carried out by BROOKFIELD standard methods and the flow curves were described by Herschel-Bulkley model. The results of dispersion analysis have shown that both the concentration of prebiotics (p=0.04<0.05) and shelf life (p=0.003<0.05) have a significant influence on the apparent viscosity of the product. Keywords—Apparent viscosity, B.lactis, consistency coefficient, flow behavior index, prebiotics. I. INTRODUCTION UNCTIONAL fermented dairy products have long been known for their value in managing intestinal disorders [1]- [3]. The different approaches are applied including the fermentation of milk with probiotics, the addition of prebiotics, and the use of synbiotics [4], [5]. The application of each treatment influences rheology and texture properties of fermented products. In addition, the interactions between probiotic strains and prebiotics are another aspect that must be considered to achieve a high viable colony forming units of bacteria and to promote the acceptable sensory properties as well viscosity at the end of the self-life of the product. Yoghurt is rheologically unstable fluid, shear thinning, which structural properties affect composition and quality of milk, way and methods of dry matter enrichment, production technology, and storage conditions [6], [7]. It is important to provide nutritional benefits, as well stability of synbiotic fermented dairy products during shelf-life. Therefore the aim of the present study was to investigate the influence of lactulose and inulin on the rheological properties of fermented milk during shelf-life. I. Beitane is with Faculty of Food Technology, Latvia University of Agriculture, Jelgava, LV-3001 Latvia (phone: 00371 63005647; fax: 00371 63005729; e-mail: Ilze.Beitane@llu.lv). I. Ciprovica is with Faculty of Food Technology, Latvia University of Agriculture, Jelgava, LV-3001 Latvia (e-mail: Inga.Ciprovica@llu.lv). II. MATERIALS AND METHODS Pasteurized milk with fat content 2.5% and the strain of Bifidobacterium lactis (Bb-12, Chr.Hansen, Denmark) were used for experiments. During the experiments, the culture was maintained at -18 o C. As prebiotics were used RAFTILINE ® HP inulin (ORAFI, Belgium) with polymerization degree ≥5 and degree of purity 99.5% and syrup of lactulose (Duphalac ® , the Netherlands) with following composition (%): lactulose – no less than 67, lactose – less than 6, galactose – less than 10. Different lactulose and inulin concentrations (1; 2; 3; 4 and 5%) were added individually to 100 g of milk. Bifidobacterium lactis was inoculated with 2 ml of milk suspension (10 6 cfu ml -1 ) and cultured at 37 o C for 16 hours. The control sample was prepared without prebiotics for comparing the obtained results. The samples of synbiotic fermented dairy products were stored at +4 o C for 7 days. The rheological properties were determined with the DV-III Ultra Rheometer BROOKFIELD rheometer equipped with thermostatistically controlled water bath TC-102 at 20.0±0.3 °C. All measurements were carried out by BROOKFIELD standard methods in three independent repeats on 1 st and 7 th day of synbiotic fermented dairy products shelf-life with controlled shear rate using a spindle SC4-16. The apparent viscosity was calculated at shear rate 7 s -1 . The flow curves were described by Herschel-Bulkley model. III. RESULTS AND DISCUSSION The apparent viscosity is relevant to content of total solids of yoghurt, i.e., with an increase of total solids in yoghurt increase the apparent viscosity [8]. The effect of lactulose on the apparent viscosity of analysed fermented milk samples is shown in Fig. 1. The obtained results have shown that the different lactulose concentrations influence the apparent viscosity of product during its shelf-life. In fermented milk samples with lactulose were observed increasing of the apparent viscosity. The apparent viscosity is lower in analysed fermented milk samples with/without lactulose than in other fermented dairy products mentioned in literature. Kulikauskiene [9] had indicated that lactulose syrup added in 2.5% concentration did not influence significantly the yoghurt apparent viscosity during shelf-life. The differences between the obtained results and those in literature given might be explained with the fact that in the present research B.lactis was used as the starter culture. Ilze Beitane, Inga Ciprovica The Study of Synbiotic Dairy Products Rheological Properties during Shelf-Life F World Academy of Science, Engineering and Technology International Journal of Nutrition and Food Engineering Vol:6, No:7, 2012 1889 International Scholarly and Scientific Research & Innovation 6(7) 2012 scholar.waset.org/1307-6892/14430 International Science Index, Nutrition and Food Engineering Vol:6, No:7, 2012 waset.org/Publication/14430